This invention relates to liquid ring pumps, and more particularly to reducing cavitation and its associated operating noise in liquid ring pumps, especially those having conical port members.
A typical liquid ring pump having conical port members is shown in Adams U.S. Pat. No. 3,289,918. Although the port members in pumps of the type shown in the Adams patent are actually frusto-conical, those skilled in the art usually refer to such port members as conical, and that terminology is also sometimes employed herein.
Cavitation sometimes occurs in conically ported liquid ring pumps, particularly those which are operated with high ratios of condensable to noncondensable vapors, at high speeds, and/or at low intake pressures (i.e., intake pressures near zero absolute pressure). Cavitation is believed to be caused by the sudden collapse or implosion of vapor bubbles near the interface between the gas being pumped and the pumping liquid (usually water) which constitutes the liquid ring. Vapor bubbles formed on the intake side of the pump may suddenly collapse when subjected to increased pressures in the compression area along with the abrupt redirection of flow which is characteristic of the discharge port area. The after-effects of the sudden collapse or implosion of these vapor bubbles may be objectionably audible outside the pump. The forces associated with numerous and repeated implosions occurring adjacent to the internal components of the pump may physically damage those components.
There are unique cavitation problems associated with conically ported liquid ring pumps. When cavitation occurs in pumps of this design, damage often concentrates at the closing edge of the discharge port. This is understandable since a portion of this edge is skewed, or sloped, in the direction of rotor rotation; thus, it constitutes the first major obstruction in the path of the compressed vapor bubbles.
Elimination of the skewed port boundary may reduce cavitation; but it would also reduce volumetric efficiency of the pump by creating a uniform duration gas discharge cycle. Conically ported liquid ring pumps rely on progressive purging (or duration discharge cycle) along the length of the discharge port member to achieve maximum volumetric efficiency. The skewed discharge port boundary is essential to achieving this result. The gas discharge cycle is of shorter duration at the end of the port member with relatively large circumference. In the foregoing description, length of the port member is measured parallel to the long axis of the rotor blades or pump shaft.
It is therefore an object of this invention to reduce cavitation in liquid ring pumps having conical port members.
It is another object of this invention to reduce the operating noise levels, and other negative effects of cavitation, in liquid ring pumps having conical port members. This is accomplished by providing for calibrated venting of vapor bubbles while retaining the gas discharge cycle whose duration varies according to the location along the main axis of the port member (i.e., parallel to the pump shaft).